Aster yellows phytoplasma subclades differentially affect resistance, infection prevalence and disease symptoms in commercial carrot

Aster Yellows phytoplasma (AYp; ‘Candidatus Phytoplasma asteris’) is an obligate
bacterial pathogen that is the causative agent of multiple diseases in herbaceous
plants. While this phytoplasma has been examined in depth for its disease
characteristics, knowledge about the spatial and temporal dynamics of pathogen
spread is lacking. The phytoplasma is found in plant’s phloem and is vectored by
leafhoppers (Cicadellidae: Hemiptera), including the aster leafhopper, Macrosteles
quadrilineatus Forbes. The aster leafhopper is a migratory insect pest that overwinters
in the southern United States, and historical data suggest these insects migrate from
southern overwintering locations to northern latitudes annually, transmitting and driving
phytoplasma infection rates as they migrate. A more in-depth understanding of the
spatial, temporal and genetic determinants of Aster Yellows disease progress will lead
to better integrated pest management strategies for Aster Yellows disease control.
Carrot, Daucus carota L., plots were established at two planting densities in central
Wisconsin and monitored during the 2018 growing season for Aster Yellows disease
progression. Symptomatic carrots were sampled and assayed for the presence of the
Aster Yellows phytoplasma. Aster Yellows disease progression was determined to be
significantly associated with calendar date, crop density, location within the field, and
phytoplasma subgroup.